Process of separating fatty acids



Patented Mar. 11, 1952 UNITED STATES i A ENT OFFICE No Drawing. Application January 28, 1949, Serial No. 73,439

(Cl. 2604l.9)

11 Claims.

This invention relates to a process for the separation of mixtures of fatty acids and in particular is directed to the separation of the fatty acids obtained by the hydrolysis or other suitable treatment of natural fats and oil into fractions of differing physical and/or chemical properties.

Heretofore two principal processes have been used for the separation of such fatty acids. One of these processes consists in pouring molten mixed fatty acids into frames; allowing the same to solidify; then enveloping the cakes of solidified acids in a cloth or other appropriate material and finally pressing the cakes under hydraulic pressure or the like to expel the liquid portion of the mixed fatty acids.

The second process comprises cooling hot solutions of such mixed fatty acids in solvents, thus allowing some of the acids to crystallize, followed by the filtration of the soluble fraction from the undissolved portion.

The first of the processes above described is in common use for the production of commercial stearic acid and red oil. This process is discontinuous and effective only for the separation of mixtures containing fatty acids which crystallize sufficiently well to allow for subsequent pressing. The second of the above processes is of broader application. It is applicable for continuous operation and may be employed to achieve a more complete separation of the fatty acids present in the mixture so that the individual fatty acids can be obtained at a higher degree of purity, if a judicious choice is made of temperature, solvent, and other operating conditions. crystals precipitated from the hot solution of the mixed fatty acids in such process occlude, entrap or otherwise carry with them substantial amounts of other materials since they are coarsely granular in structure, thus resulting in the recovery of fatty acids which are contaminated by the more soluble constituents of the original fatty acid mixture. If the crystallization is effected so as to obtain very fine grains the subsequent filtration becomes very difficult or even impossible of accomplishment.

Another disadvantage of such process is the necessity of employing rather high temperatures for the preparation of the solution of the mixed fatty acids and therefore of working under conditions by which, if alcohol is used as the solvent, part of such solvent is lost through the formation of fatty acid esters resulting from the esterification of the alcohol and the fatty acids.

My invention permits of the separation of the However, the

mixed fatty acids at temperatures which are considerably below those required for the solu-- tion of mixtures of fatty acids and provides for a substantial reduction in the amount of diluent retained by the crystals. Another advantage of my invention resides in the fact that under comparable conditions, i. e., if the same mixtures of fatty acids are employed and finished products of the same characteristics are produced, considerably less solvent is required for the separation of the mixed fatty acids than that required in carrying out any of the prior processes having the same purpose and employing the same solvents. This is an important feature, especially from the point of view of economy, since the entire amount of the solvent used must eventually be evaporated. Another advantage of my invention is the facility which it offers for continuous operation, as it is readily adaptable for continuously operating appartus. This i in contrast with the prior process wherein it is difficult, or almost impossible, to avoid interruptions if solutions of mixed fatty acids have to be prepared, brought to certain concentrations, etc. Furthermore, my novel process obviates all interruptions connected with the control of the velocity of crystallization, formation of crystals of requisite size and other details of the former processes.

Accordingly, one of the principal objects of this invention is the provision of a process for the separation of mixtures of fatty acids into fractions of different solubilities and the separation thereof.

Another object of my invention is the provision of a process for the separation of fatty acids into fractions of different solubilities with resultant separation of the non-soluble fraction that contains but a minimum of entrained solvent or other diluent.

Another object of my invention is the provision of a process for the separation of fatty acids into fractions of different solubilities with consequent economies in the use of the solvents.

In its fundamental aspect my invention comprises the steps of vigorously stirring and supercooling a mixture of liquid fatty acids whereby a semi-fluid magma containing very fine crystals is obtained; then mixing such magma with a cold solvent so as to obtain a liquid phase of low titer fatty acids dissolved in the solvent and a crystalline phase of undissolved high titer fatty acids; then separating the liquid phase from the crystalline or solid phase; and finally recovering from each of those phases, by removal of the solvent, the fatty acids thereof.

The production of such a semi-fluid magma we a may be accomplished by using any suitable apparatus conventionally employed in eflectuating thorough stirring or agitation and cooling of viscous materials, as for example, a water-cooled crutcher having an automatic discharging device. Under such conditions of agitation and cooling it is possible to cool the mixture considerably below its normal freezing point before it loses the consistency required for mechanical discharge and transport by means of rotating screws and the like, and therefore to facilitate the continuous discharge into apparatus where the magma is brought into contact with a solvent. As an example of such apparatus, it may be noted that there may be used a centrifugal machine provided with cooling coils and a scraper for the continuous discharge of the separated solid particles deposited on the walls by centrifugal action. The apparatus per so does not form a part of my invention and in place of the apparatus above described there may be used any other suitable continuous filtering apparatus, and indeed even discontinuous filters working by suction or pressure or the like may be employed.

The temperature of the solvent brought in contact with the magma is regulated in such a way that the temperature of the resulting mixture is that which is most favorable for obtaining the desired product. For example, if it is desired to effectuate a separation at C. and the temperature of the magma is C., the temperature of the solvent must be considerably under 10 C. and it will be adjusted to the proper temperature depending upon the ratio between the weights of the magma and the solvent employed.

Although not indispensable, it is preferable to use a pre-cooled solvent inasmuch as it is advantageous to avoid cooling of the mixture of the magma and the solvent. Subsequent cooling of the magma and the solvent results in spontaneous I crystallization of small quantities of fatty acids which went into solution at the higher temper ature and the magma becomes admixed to some extent with these later produced crystals which may interfere with filtration, and also may be likely to occlude or entrain diluents as in the case of the previously described known process.

I have discovered that if the temperature of the solvent is such that it is not necessary subsequently to cool the mixture of the solvent and the magma, the filtration is facilitated, but I wish to point out that this does not exclude the use of apparatus provided with cooling devices allowing for the regulation of the temperature. Furthermore, it should also be noted that this process does not exclude operations under such conditions where further cooling may be advisable, especially since the solubility at low temperatures of most of the fatty acids is insignificant and therefore that the amount of crystals formed on such eventual cooling is not great enough to cause serious difficulties. It is also to be noted that the mixing of the solvent with the magma may be carried out in two or more stages. The first consisting in adding a portion (one-third or less of the total amount should be employed) of the solvent cooled to a temperature which is equal or slightly lower than that of the magma, whereas the remainder of the solvent is later added after it is cooled to a much lower degree. Operation in this fashion may be found advantageous if, for example, the starting material contains only a small amount of liquid fatty acids and therefore has a tendency to solidify to hard or stonelike blocks when brought in contact with very cold solvent. Other types of fatty acids containing considerable amounts of liquid fatty acids crumble promptly on addition of the solvent because the liquid fatty acids are of practically unlimited solubility. This is not the case With fatty acids which are poor in liquid fatty acids.

The advantages offered by my invention for efiectuating the separation of the fatty acids by employing less of the solvent than has heretofore been the case, and likewise for obtaining crystals which retain less solvent than has heretofore been possible by the use of crystallization procedures may be demonstrated by the following experiments.

Experiment I (a) grams of palm oil fatty acids are dissolved by heating in 100 grams of methanol and then cooled slowly to 5 C. A nearly solid mass is formed of intricate crystals from which none, or nearly none, of the solution can be removed by suction under reduced pressure.

(1)) The same quantity of the same molten fatty acids are brought to 20 C. by cooling with simultaneous vigorous stirring, and then there is mixed therewith 100 grams of methanol having a temperature of 15 C. and the mixture then cooled to 5 C. This mixture allows for the comparatively very easy separation of the liquid phase.

Experiment I] (a) 100 grams of the mixed fatty acids of Experiment I are dissolved in 300 grams of methanol and cooled to 5 C. The crystals formed on cooling are then filtered by suction in such way that there is no, or nearly no, loss of solvent and the remaining crystals are immediately weighed. The solvent is then evaporated from the crystals and the weight thereof calculated by difference and reported with respect to the weight of the crystals as first obtained.

(b) An analogous experiment Was made employing a magma obtained from 100 grams of the same fatty acids by vigorous stirring until the temperature was reduced to 20 C.; mixing the magma with 300 grams of methanol having a temperature of 15 C.; subsequently cooling the mixture to 5 C.; and filtering and weighing the separated crystals under exactly the same conditions as above. The quantity of solvent retained, reported with respect to the Weight of the crystals as first obtained is found to be only about one-third of that of part a of this experiment.

A modification of the process consists in replacing the solvent by solutions of fatty acids in one or several of the solvents as they are obtained from the second, third or subsequent extractions of the above described magmas with the pure or virgin solvents.

A further modification of the process of this invention consists in adding to the mixed fatty acids finely divided inert materials such as kaolin, neutral salts, textile fibers and the like and then treating the same in accordance with the process. The addition of such inert materials in relatively small quantities of from 5% to 20% by weight of the mixed fatty acids results in the maintenance of the desired consistency (suitable for mechanical transport) of the magma at temperatures lower than in the case where the inert materials are not present; and also aids in the subsequent filtration.

There may be used as solvents in carrying out drocarbons such as benzine, benzol and other solvents for fatty acids.

The following are illustrative examples for carrying out my invention.

Example I 100 parts of palm oil fatty acid (iodine value 50,'titer 42 C., 95% free fatty acids, hereinafter designated FFA) are molten, cooled under vigorous stirring to 20 C. and mixed with 100 parts of methanol having a temperature of 15 C. The mixture is cooled to 5 C. while being vigorously agitated and then filtered by suction or pressure. The residue on the filter is stirred up in two subsequent operations, each time with 50 parts of methanol at from C. to C. and separated in the same way from the solute. The adhering solvent is then evaporated, leaving about 42 parts of fatty acid having a titer of from 56 C. to 57 C. and an iodine value of from 3 to 4. The filtrates of the first and second filtration are concentrated until their alcoholic content is reduced to about.25%; cooled to 0 C. and the precipitate formed thereby filtered off. This filtered residue constitutes a fatty acid the titer of which is about the same as that of the original fatty acid and may be employed for subsequent operations. The filtrate, after evaporation of the solvent, leaves a technical red oil having a titer of about C. Thefiltrate from the third filtration may be treated in the same way or employed in the place of pure methanol for the initial separation of a new batch of cooled mixed fatty acids.

Example II 80 parts of tallow fatty acids and parts of palm oil fatty acids (as in Example I) are cooled under vigorous stirring to 22 C. To this magma so produced there is added 20 parts of mother liquor (the liquid resulting from the second, third or further extraction of the separated high titer fatty acids of a previous operation) and the mixture cooled under stirring to 0 C. To it is added 100 parts of the same mother liquor at 0 C., continuing the stirring and centrifugating. The separated liquor is cooled to minus C. Upon evaporation of the solvent therefrom there is obtained a commercial red oil having a titer of 10 C. The centrifuge residue is stirred up in three subsequent operations with 50, 40 and parts of methanol respectively at 0, 3, and 5 C., being centrifuged after each operation. The fatty acid centrifuge residue, after evaporation of the solvent, is a stearine having a titer of 54 C. and an iodine value of 4.5. The separated liquors serve as a solvent for a subsequent operation.

Example III 100 parts of palm oil fatty acid, as in Example I, are molten and cooled in accordance with the rocedure described in Example I and then treated with 120 parts of a solution obtained by the second and/or third filtration from a previous operation carried out in accordance with the process described in Example I and the separation of the insoluble portion eifectuated at from 5 C. to 8 C. The residue is treated by two or three subsequent operations, each time with from 50 to 60 parts of-methanol at a temperature ranging between 10 C. and 0 C. This residue then yields, after elimination of the solvent, about 45 parts of a product containing about of palmitic acid having an iodine value of about 5 to 6 and a titer of from 55 C. to 56 C.

' Example IV 90 parts of tallow fatty acid are mixed intimately with 10 parts of salt (NaCl) and then transformed into a pasty state as described in the preceding examples. The pasty mass is then treated three to four times, at temperatures ranging between 15 C. and 0 C., with various quantitles of solvent, the total amount of the latter being about 250 parts. Solid and liquid phase are each time separated by filtration. The resultant fatty acid is separated from the salt by centrifugation at elevated temperature or by extraction with hot methanol or benzine. The final product is technical stearine having a titer of from 54 C. to 55 C.

Example V parts of shea-butter fatty acid (iodine value 50, titer 45 C., 96% free fatty acids) are molten, cooled under vigorous stirring to 25 C. and mixed with 25 parts of methanol having a temperature of 15 C. To the mixture thus produced there are added '75 parts of methanol having a temperature of 0 C. The mixture having now a temperature of about 12 C. is cooled to 0 C. and then filtered. The residue is treated in three consecutive operations, each time with 50 parts of methanol at temperatures ranging between 0 and 5 C., and each time filtered off. This residue then yields, after elimination of the solvent, about40 parts of a fatty acid having an iodine value of 4 to 5 and a titer of from 63 to 64 C.

Example VI 100 parts of palm oil fatty acids, as in Example I, are molten and cooled in accordance with the procedure. described in Example I to a temperature of 20 C. To the magma thus produced there are added 20 parts of ethanol containing 10% of Water and the mixture thus obtained is cooled to 0 G. Then 100 parts of a solution obtained by the second (and/or third) subsequent filtrations of the previous operation carried out in the same manner using the diluted alcoho1 as described in the present example, are added and the separation carried out at 0 C. The residue is then stirred up in two or three subsequent treatments each time with from 50 to 60 parts of ethanol containing 10% water and filtered off at 0 C. The final product is the same as the palmitic acid described as the end product of Example III.

In carrying out my process I have found that effective separations of the mixed fatty acids may be obtained by using quantities of solvents ranging from about 80% by weight of the mixed fatty acids up to about from 300 to 400%. It will be understood that the solvent may be used in a single solubilizing charge or subdivided into two, three or more fractions depending upon the number of consecutive treatments desired. The number of treatments may be selected, it will be obvious, depending upon the thoroughness of the separation desired and the particular mixture of fatty acids being subjected to separation.

The mixed fatty acids can be super-cooled under vigorous stirring to temperatures of from about 15 C. to 20 0. below the titer or such mixed fatty acids (as determined by conventional methods) and retain a fluidity or liquidity sufllcient for mechanical transport. For example, tallow fatty acids of 43 C. titer are easily under-cooled to 25 C.

It will also be understood that the most effective temperatures at which separations can be effectuated will depend upon the particular mixture of fatty acids and the particular solvents being used.

With my principle established, the skilled chemist will be able readily to select the appropriate degree of super-cooling and temperature of the solvent used by relatively simple tests which can be quickly and easily made in the laboratory. In general it may be stated that the pasty, crystalline, viscous mass of the supercooled fatty acids is effectively converted upon the addition thereto of the solvent having a temperature ranging from about minus 10 C. to plus 10 0., into two relatively sharp phasesa solid phase and a liquid phase.

It will further be understood that the foregoing examples are but illustrative of the means for carrying my invention into practice and accordingly the appended claims are to be understood as defining my invention within the full spirit and scope thereof.

I claim:

1. Process of separating a mixture of fatty acids into fractions of different solubilities which comprises mechanically stirring and slowly cooling the mixture to a temperature of about to C. below the titre of the mixed fatty acids whereby a pasty crystalline mass of high viscosity is formed and mixing said pasty mass with a selective solvent which possesses at the employed temperatures selective solvent power for unsaturated constituents and separating the solid phase from the liquid phase.

2. Process in accordance with claim 1 wherein the mixture of the pasty crystalline mass with the solvent i cooled to a temperature of not less than about minus 10 C. before proceeding to the separation of the solid phase from the liquid phase.

3. Process in accordance with claim 1, wherein the solvent to be added to the pasty crystalline mass is previously cooled to a temperature below that of the said mass.

4. Process in accordance with claim 1, comprising the mixture with the mixed fatty acids, prior to the slow cooling thereof, of a finely divided inert material.

5. Process of separating a mixture of fatty acids into fractions of different solubilities which comprises adding a portion of a solvent for the unsaturated constituents of said mixture of fatty acids, said portion being between 15 and 50% of the weight of the fatty acids, mechanically stirring and slowly cooling the so formed mixture to a temperature of about 15 to 20 C. below the titre of the mixed fatty acids whereby a pasty crystalline mass of high viscosity is formed, adding the balance of the solvent required to dissolve the unsaturated constituents of said mixed fatty acids, and separating the solid phase from the liquid phase.

6. Process in accordance with claim 5 wherein the said portion of the solvent amounting to between 15 to 50% of the weight of the fatty acids is added to the mixture of fatty acids at any time during the period commencing before and extending through the stage of producing the pasty crystalline mass, to maintain same in viscous condition, at a temperature which is equal or below that of the said mass.

7. Process in accordance with claim 6 wherein the mixture of the crystalline mass and the solvent is cooled to a temperature of not less than about minus 10 C. before proceeding to the separation of the solid phase from the liquid phase.

8. Process in accordance with claim 5 wherein the rest of the solvent before being added to the pasty crystalline mass containing the fatty acids and a portion of the solvent, is cooled to a temperature below that of the said mass.

9. Process in accordance with claim 8 wherein the mixture of the crystalline mass and the solvent is cooled to a temperature of not less than about minus 10 C., before proceeding to the separation of the solid phase from the liquid phase.

10. Process in accordance with claim 5 wherein the mixture of the crystalline mass and the solvent is cooled to a temperature of not less than about minus 10 C. before proceeding to the separation of the solid phase from the liquid phase.

11. Process in accordance with claim 5, comprising the mixture with the mixed fatty acids, prior to the slow cooling thereof, of a finely divided inert material.

ERNEST SCHLENKER.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,012,106 Mauersberger Aug. 20, 1935 2,113,960 Grote et al. Apr. 12, 1938 2,293,676 Myers et al. Aug. 18, 1942 2,298,501 Myers et al Oct. 13, 1942 2,505,012 Spannuth Apr. 25, 1950 OTHER REFERENCES Foreman: Oil 8: Soap, July 1944, pp. 183-487. 

1. PROCESS OF SEPARATING A MIXTURE OF FATTY ACIDS INTO FRACTIONS OF DIFFERENT SOLUBILITIES WHICH COMPRISES MECHANICALLY STIRRING AND SLOWLY COOLING THE MIXTURE TO A TEMPERATURE STIRRING AND SLOWLY COOLING THE BELOW THE TITRE OF THE MIXED FATTY ACIDS WHEREBY A PASTY CRYSTALLINE MASS OF HIGH VISCOSITY IS FORMED AND MIXING SAID PASTY MASS WITH A SELECTIVE SOLVENT WHICH POSSESSES AT THE EMPLOYED TEMPERATURES SELECTIVE SOLVENT POWER FOR UNSATURATED CONSTITUENTS AND SEPARATING THE SOLID PHASE FROM THE LIQUID PHASE. 